Sulfur vulcanization of Styrene/Butadiene/Styrene block copolymers and Styrene/Butadiene Rubber (SBR) to improve the mechanical properties of polymer/asphalt admixtures is known to those skilled in the art. Specifically, U.S. Pat. No. 3,803,066 discloses a modified bitumen prepared by blending a powder or latex of rubber (natural or synthetic) into the bitumen at 125-160.degree. C. and adding sulfur and a vulcanization accelerator (e.g. organic peroxide) to this mixture in a ratio of sulfur to rubber of 0.3 to 0.9. Said modified bitumen is homogeneous and ductile at low temperatures. U.S. Pat. No. 3,634,293 discloses compositions containing bitumen, olefin polymers (e.g ethylene acrylate), a base (e.g. metal salt of an oxide, hydroxide, sulfide, carbonate or silicate) and sulfur. The order of addition can be bitumen plus polymer followed by sulfur addition or all together. Said composition is said to be homogeneous and elastic. U.S. Pat. No. 3,992,340 discloses vulcanized molding compositions comprising bitumen and olefin polymers and sulfur. These molding compounds have a 2:1 to 1:1 weight ratio of bitumen to olefin polymer. Various orders of addition of ingredients were disclosed including (i) bitumen plus sulfur and a vulcanization accelerator, these are then added to the olefin (e.g. styrene/butadiene) polymer (ii) bitumen olefin polymer and sulfur mixed all together, and cured by the vulcanization accelerator addition, (iii) mixing bitumen, olefin polymer, sulfur, a vulcanization accelerator all together and (iv) prepare a homogeneous mixture of an olefin polymer, sulfur and a vulcanization accelerator, followed by mixing the homogeneous mixture with bitumen. U.S. Pat. No. 4,130,516 discloses the addition of 3-7% sulfur into asphalt to increase ductility. A small amount (0.5-1.5%) of SOLPRENE.RTM. 1206 (a linear random styrene/butadiene copolymer) is added to further increase ductility.
U.S. Pat. No. 4,412,019 discloses the use of a hydrogenated styrene/butadiene rubber (e.g Solprene 512--a substantially linear butadiene/styrene block copolymer coupled with epoxidized soy bean oil) with sulfur for improving the temperature stability of asphalt. The hydrogenated styrene/butadiene rubber is used at a level of 5-20% and the sulfur is used at a level of 1-40% sulfur in the asphalt. The polymer has a molecular weight of 70,000.
U.S. Pat. Nos. 4,145,322, 5,314,935, 5,371,121, all disclose bitumen/polymer compositions wherein bitumen and di or tri block copolymers are blended together, and then the sulfur, or sulfur plus vulcanization accelerator, is added to the bitumen/ polymer blend.
U.S. Pat. No. 4,242,246 discloses a process for the preparation of bituminous compositions making use of a mother solution containing styrene/butadiene block co-polymers and sulfur in a petroleum solvent. The polymers are block copolymers of styrene and butadiene of molecular weight 30,000 to 300,000, preferably between 70,000 and 200,000. Said styrene/butadiene block co-polymer is premixed with sulfur (2 to 6% by weight to the polymer) into a petroleum solvent. The styrene/butadiene block polymer/sulfur/solvent mixture is blended into the asphalt.
U.S. Pat. No. 4,554,313 discloses a process for preparing bitumen-polymer compositions comprising the use of organic sulfur compounds, such as ditertiododecyl or dinonyl pentasulphide. The polymers are random or block copolymers of styrene and butadiene of molecular weight 30,000 to 300,000, preferably between 70,000 and 200,000. The sulfur compound and co-polymer are dissolved into a hydrocarbon oil, and then added to the asphalt.
U.S. Pat. No. 4,576,648 discloses cationic emulsions of bituminous binders of the bitumen type comprising cationic asphalt emulsions prepared using the polymer modified asphalt disclosed in U.S. Pat. No. 4,554,313.
U.S. Pat. No. 5,672,642 discloses a process for preparing storage stable asphalt/polymer blends prepared by contacting elemental sulfur with asphalt to form a blend. Said elemental sulfur/asphalt blend is added to the polymer. The preferred polymers are diene block copolymers such as styrene/butadiene/styrene and styrene/isoprene/styrene.
Additionally, styrene/butadiene rubber latex containing sulfur and/or a vulcanization accelerator is commercially available as BUTONAL.RTM. NX 1106x and ULTRAPAVE.RTM. 5061. The sulfur and vulcanization accelerator were simply added to the latex.
Applicants have discovered that an aqueous sulfur dispersion, with or without a vulcanization accelerator, can be co-agglomerated with the SBR base latex for the preparation of the high solids sulfur co-agglomerated SBR latex. Surprisingly, the sulfur co-agglomerated SBR latex is easier to mix with the asphalt and either reduces or totally eliminates separation of the polymer rich layer during storage at elevated temperature (e.g. 160.degree. C. to 180.degree. C. for 2 to 3 days). Further, if separation occurs, it is easily re-mixed with gentle agitation. Thus, the polymer-asphalt admixture prepared with the sulfur co-agglomerated SBR latex maintains homogeneity. Further, Applicants' method requires no petroleum solvents and less sulfur is required.
Finally, since the SBR latex polymer/sulfur agglomerate is storage stable, it is easily blended with the asphalt on the job site, alleviating the compatibility problems associated with polymer modified asphalts.